Conventionally, radiographs using films have been widely used in clinical settings. However, information provided by the radiographs using films are analog image information, and thus, digital radiation detectors such as a computed radiography (CR) detector, a flat panel detector (hereinafter referred to as “FPD”) and the like have been developed in recent years.
In a FPD, a scintillator panel is used to convert radiation into visible light. The scintillator panel includes a scintillator layer containing a radiation phosphor such as gadolinium oxysulfide (hereinafter referred to as “GOS”) or cesium iodide (hereinafter referred to as “CsI”), and the phosphor emits visible light in response to the applied radiation. The emitted light is then converted into an electrical signal by a TFT or a CCD, and as a result, the radiation information is converted to digital image information. At this time, if the energy of the radiation to be applied is increased in order to improve the luminance of the scintillator panel, the emission intensity of the phosphor is also increased. However, in order to reduce the amount of radiation exposure to a subject or the like, on the other hand, it is required to utilize the light emitted by the phosphor at a high efficiency, without excessively increasing the energy of the radiation to be applied.
One of the causes of the reduction in the utilization efficiency of the light emitted by the phosphor is that the emitted light is scattered due to the phosphor itself, as a result of which the emitted light is absorbed within the scintillator layer. In order to reduce the scattering of light, a technique has been proposed in which particles having a high refractive index comparable to the refractive index of the phosphor are incorporated into the scintillator layer (Patent Document 1).